Clutch

ABSTRACT

A clutch is provided with a drive-side rotational body and a driven-side rotational body, which is movable in the axial direction of the drive-side rotational body between a coupled position. The driven-side rotational body has a groove having a helical portion and an annular portion. The clutch also includes an urging member and a pin that is selectively inserted into and retracted from the groove. The clutch moves the driven-side rotational body to the decoupled position against the urging force of the urging member by inserting the pin in the helical portion. The clutch further includes a restricting portion that restricts shifting of the position of the pin from the annular portion to the helical portion when the pin is positioned in the annular portion.

TECHNICAL FIELD

The present disclosure relates to a clutch that switches the state ofpower transmission from a drive-side rotational body to a driven-siderotational body by switching the coupling state of the driven-siderotational body with respect to the drive-side rotational body.

An engine is known that couples a mechanical pump, which circulatescoolant, to the crankshaft through a clutch to operate the pump usingrotational force of the crankshaft and disengages the clutch to stopoperation of the pump. Clutches for switching the coupling state of thepump with respect to the crankshaft include a clutch having a drive-siderotational body coupled to the crankshaft and a driven-side rotationalbody, which is rotational relative to the drive-side rotational body.The clutch is maintained in the engaged state by pressing the rotationalbodies against each other using magnetic force of magnets.

Such clutches include a clutch described in Patent Document 1. Theclutch described in Patent Document 1 includes a coil. To disengage theclutch, energization control is performed on the coil to generate amagnetic field that cancels the aforementioned magnetic force.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: Japanese Laid-Open Patent Publication No. 2010-203406

SUMMARY OF THE INVENTION

Problems that the Invention is to Solve

In a configuration in which the clutch is maintained in the engagedstate by pressing the drive-side rotational body and the driven-siderotational body against each other as described in Patent Document 1,the force needed for such pressing becomes greater as the torque thatneeds to be transmitted through the clutch, or, in other words, thetorque needed by an auxiliary device driven and rotated by thedriven-side rotational body, becomes greater. To increase the pressingforce, magnets with a greater magnetic force must be employed. Thisnecessitates a larger-sized coil to cancel the magnetic force.

The larger-sized coil enlarges the size of the clutch and increasespower consumption. Therefore, the force needed for disengagement istherefore desired to be minimized while ensuring transmission of greattorque.

This problem is not restricted to clutches that cancel magnetic force ofmagnets by generating a magnetic field as in the above-described case.The same problem is generally present in clutches that are disengaged bycausing relative movement between a drive-side rotational body and adriven-side rotational body with an actuator, such as clutches that aredisengaged using hydraulic pressure.

Accordingly, it is an objective of the present disclosure to provide aclutch that can be disengaged by a small force.

Means for Solving the Problems

To achieve the foregoing objective and in accordance with one aspect ofthe present invention, a clutch is provided that includes a drive-siderotational body, a driven-side rotational body, an urging member, agroove, a pin, and a restricting portion. The driven-side rotationalbody is movable in an axial direction of the drive-side rotational bodybetween a coupled position at which the driven-side rotational body iscoupled to the drive-side rotational body and a decoupled position atwhich the driven-side rotational body is decoupled from the drive-siderotational body. The urging member urges the driven-side rotational bodyfrom the decoupled position toward the coupled position. The groove isformed in an outer circumferential surface of the driven-side rotationalbody. The groove has a helical portion that extends about an axis of thedriven-side rotational body and an annular portion that is formedcontinuously from the helical portion and extends over an entirecircumference of the driven-side rotational body and perpendicularly tothe axial direction. The pin is selectively inserted into and retractedfrom the groove and restricted from moving in the axial direction. Whenthe pin is in a state inserted in the helical portion and engaged with aside wall of the helical portion, the position of the pin is shiftedfrom the helical portion to the annular portion through rotation of thedriven-side rotational body such that the driven-side rotational body ismoved to the decoupled position against urging force of the urgingmember. The restricting portion restricts shifting of the position ofthe pin from the annular portion to the helical portion when the pin isin a state located in the annular portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a clutch according to a firstembodiment;

FIG. 2 is a side view showing the clutch shown in FIG. 1 in a disengagedstate;

FIG. 3 is a side view showing the clutch of FIG. 1 in an engaged state;

FIG. 4 is a cross-sectional view illustrating the relationship between agroove of a driven-side rotational body and a stopper member and theconfiguration of an actuator for operating the stopper member;

FIG. 5 is a side view showing a clutch according to a second embodimentin a disengaged state;

FIG. 6 is a side view showing the clutch illustrated in FIG. 5 in anengaged state;

FIG. 7 is a developed view showing a groove of the clutch of FIG. 5;

FIG. 8 is a side view showing a clutch according to a third embodimentin a disengaged state;

FIG. 9 is a side view showing the clutch illustrated in FIG. 8 in anengaged state;

FIG. 10 is a developed view showing a groove of the clutch of FIG. 8;

FIG. 11 is a developed view showing a groove of a modification of thethird embodiment;

FIGS. 12A, 12B, 12C, and 12D are schematic diagrams illustrating changeof the state of a clutch according to a fourth embodiment;

FIGS. 13A, 13B, 13C, and 13D are schematic diagrams illustrating changeof the state of a clutch according to a fifth embodiment; and

FIG. 14 is a perspective view showing a driven-side rotational bodyaccording to another embodiment.

MODES FOR CARRYING OUT THE INVENTION First Embodiment

A clutch according to a first embodiment will now be described withreference to FIGS. 1 to 4.

A clutch according to a first embodiment switches the state of powertransmission from a crankshaft arranged in an engine to a water pump,which circulates coolant of the engine.

As shown in FIG. 1, a clutch 100 of the first embodiment is accommodatedin an accommodating portion 310, which is arranged in a housing 300. Asubstantially cylindrical support member 320 is fitted in the housing300. An output shaft 210 of the clutch 100 is rotationally supported bythe support member 320 through a first bearing 330, which is located atan inner circumferential side of the support member 320.

An impeller 220 of a pump 200 is attached to a distal end portion (aright end portion as viewed in FIG. 1) of the output shaft 210 in amanner rotational integrally with the output shaft 210. A drive-siderotational body 110 is rotationally supported by a proximal end portion(a left end portion as viewed in the drawing) of the output shaft 210through a second bearing 340. A straight spline 212 is formed in anouter circumferential surface of a portion of the output shaft 210between the first bearing 330 and the second bearing 340.

With reference to FIG. 1, a driven-side rotational body 120 is arrangedbetween the housing 300 and the drive-side rotational body 110. Anengagement portion 121, which is meshed with the straight spline 212 ofthe output shaft 210, is formed in an inner circumferential surface ofthe driven-side rotational body 120. This configuration allows thedriven-side rotational body 120 to rotate integrally with the outputshaft 210 and move in the axial direction of the output shaft 210. Inthe first embodiment, as represented by the long dashed short dashedlines in FIGS. 1 to 3, the output shaft 210, the drive-side rotationalbody 110, and the driven-side rotational body 120 are arranged coaxiallywith one another. Hereinafter, the extending direction of the axis ofthese components will be referred to as the axial direction.

The driven-side rotational body 120 has an outline including two columnsthat have different diameters and are joined coaxially with each other.The driven-side rotational body 120 is supported by the output shaft 210in such an orientation that a large diameter portion 122 is located onthe side close to the drive-side rotational body 110 (a left side asviewed in FIG. 1) and a small diameter portion 123 is arranged on theside close to the pump 200 (a right side as viewed in the drawing).

A recess 124 having an opening facing the pump 200 is formed in thesmall diameter portion 123 of the driven-side rotational body 120. Aplurality of accommodating recesses 125 for accommodating urging members135 are formed in a bottom portion of the recess 124. The accommodatingrecesses 125 are arranged circumferentially in a manner surrounding theoutput shaft 210.

Each of the urging members 135 is, for example, a coil spring andaccommodated in the corresponding one of the accommodating recesses 125.Each urging member 135 has a distal end secured to a securing projection211, which projects from the output shaft 210. The urging members 135are accommodated in the corresponding accommodating recesses 125 each ina compressed state and urge the driven-side rotational body 120 towardthe drive-side rotational body 110 (leftward as viewed in FIG. 1).

A plurality of ball accommodating grooves 127 each for accommodating acorresponding one of balls 130 are formed in the large diameter portion122 of the driven-side rotational body 120 and arrangedcircumferentially. An arcuate groove 111, which extends over the entirecircumference of an inner circumferential surface of the drive-siderotational body 110, is formed in the inner circumferential surface ofthe drive-side rotational body 110. With reference to FIG. 1, thearcuate groove 111 has an arcuate cross section. Each of the balls 130is accommodated in the space formed by the corresponding one of the ballaccommodating grooves 127 and the arcuate groove 111.

When the driven-side rotational body 120 is arranged at the positionillustrated in FIG. 1 after having been moved toward the drive-siderotational body 110 by the urging force of the urging members 135, thedrive-side rotational body 110 and the driven-side rotational body 120are coupled to each other through the balls 130.

Hereinafter, out of axial positions of the driven-side rotational body120 moving axially along the output shaft 210, the position at which thedrive-side rotational body 110 and the driven-side rotational body 120are coupled to each other, as illustrated in FIG. 1, will be referred toas a coupled position.

A cup-like driven-side pulley 270, which surrounds the clutch 100accommodated in the accommodating portion 310 of the housing 300, isattached to the drive-side rotational body 110. A drive-side pulley 260is attached to an end portion of the crankshaft 250 in a mannerrotational integrally with the crankshaft 250. The drive-side pulley 260and the driven-side pulley 270 are coupled to each other through a belt280, which is looped over the drive-side pulley 260 and the driven-sidepulley 270.

As a result, as illustrated in FIG. 1, when the driven-side rotationalbody 120 is arranged at the coupled position and the drive-siderotational body 110 and the driven-side rotational body 120 are coupledto each other through the balls 130, rotation of the crankshaft 250 istransmitted to the driven-side rotational body 120 and the output shaft210 via the drive-side pulley 260 and the belt 280. This causes theimpeller 220, which rotates integrally with the output shaft 210, tosupply coolant out from the pump 200. As represented by the arrows inFIGS. 2 and 3, the drive-side rotational body 110 rotates in a clockwisedirection as viewed from the side corresponding to the distal end of theoutput shaft 210 (the side corresponding to the right end as viewed inFIGS. 2 and 3) toward the drive-side rotational body 110.

Referring to FIGS. 2 and 3, each of the ball accommodating grooves 127,which are formed in the large diameter portion 122 of the driven-siderotational body 120, extends in the axial direction from an end surfaceof the large diameter portion 122 before being curved and then extendsin the rotational direction of the drive-side rotational body 110. Afinishing end of each ball accommodating groove 127 forms a holdingportion 128.

The depth of each ball accommodating groove 127 becomes smaller in therotational direction of the drive-side rotational body 110 such that thedepth of the holding portion 128 is minimized.

As a result, as illustrated in FIG. 2, when each ball 130 isaccommodated in the axially extended portion of the corresponding ballaccommodating groove 127, a clearance in which the ball 130 is permittedto rotate, together with the driven-side rotational body 120, withrespect to the drive-side rotational body 110 is formed between the ballaccommodating groove 127 and the arcuate groove 111 (see FIG. 1) of thedrive-side rotational body 110.

In contrast, as illustrated in FIG. 3, when each ball 130 is located inthe corresponding holding portion 128 after having been moved in theball accommodating groove 127, the clearance between the holding portion128 and the arcuate groove 111 (see FIG. 1) of the drive-side rotationalbody 110 is small. The ball 130 is thus caught between the driven-siderotational body 120 and the drive-side rotational body 110. Thisrestricts rotation of the ball 130 together with the driven-siderotational body 120 with respect to the drive-side rotational body 110.

In this manner, the balls 130 are non-rotational when the driven-siderotational body 120 is arranged at the coupled position illustrated inFIG. 3. This allows the driven-side rotational body 120 to rotatetogether with the drive-side rotational body 110. That is, when thedriven-side rotational body 120 is located at the coupled position, theballs 130 are caught between the driven-side rotational body 120 and thedrive-side rotational body 110 in a non-rotational manner, thus couplingthe driven-side rotational body 120 to the drive-side rotational body110.

In contrast, when the driven-side rotational body 120 is arranged at theposition illustrated in FIG. 2, the balls 130 are released from theholding portions 128 and received in the axially extended portions ofthe corresponding ball accommodating grooves 127. Specifically, asubstantially half of each ball 130 is accommodated in the arcuategroove 111 of the drive-side rotational body 110. This restricts axialmovement of the ball 130 relative to the drive-side rotational body 110.When each ball 130 is received in the axially extended portion, whichhas a depth greater than the depth of each holding portion 128, afterhaving been released from the holding portion 128 with a smaller depth,the ball 130 is released from the driven-side rotational body 120 andthe drive-side rotational body 110. As a result, the drive-siderotational body 110 and the driven-side rotational body 120 are allowedto rotate relative to each other. That is, the driven-side rotationalbody 120 is decoupled from the drive-side rotational body 110.

Hereinafter, out of the axial positions of the driven-side rotationalbody 120 moving axially along the output shaft 210, the position atwhich the drive-side rotational body 110 and the driven-side rotationalbody 120 are decoupled from each other as illustrated in FIG. 2 will bereferred to as a decoupled position.

As illustrated in FIG. 2, a circumferential groove 400 is formed in anouter circumferential surface of the small diameter portion 123 of thedriven-side rotational body 120. The groove 400 includes a helicalgroove 410 serving as a helical portion extending about the axis in amanner inclined with respect to the axial direction and an annulargroove 420 serving as an annular portion extending perpendicular to theaxial direction. The helical groove 410 extends in a manner revolving onthe outer circumferential surface of the driven-side rotational body 120by one cycle and inclined such that the helical groove 410 approachesthe drive-side rotational body 110 toward the trailing end in therotational direction of the drive-side rotational body 110. The annulargroove 420 is formed continuously from the helical groove 410 andextends over the entire circumference of the outer circumferentialsurface of the driven-side rotational body 120. The configuration of thegroove 400 will be described in detail below.

With reference to FIGS. 2 and 3, the clutch 100 includes a lockingmember 140 and an actuator 150 for selectively inserting and retractinga pin 141, which is arranged at the distal end of the locking member140, with respect to the groove 400. The axial position of the lockingmember 140 is restricted. As illustrated in FIG. 3, the axial positionof the locking member 140 is set such that the pin 141 is inserted intoa portion of the helical groove 410 of the groove 400 in the vicinity ofa starting end 411 when the driven-side rotational body 120 is arrangedat the coupled position. If the locking member 140 is operated by theactuator 150 to move toward the driven-side rotational body 120 when thedriven-side rotational body 120 is located at the coupled position, thepin 141 is inserted into the portion of the helical groove 410 in thevicinity of the starting end 411. After having been inserted into thehelical groove 410, the pin 141 is engaged with a side wall 413 of thehelical groove 410, thus locking the driven-side rotational body 120against the urging force of the urging members 135.

If the pin 141 of the locking member 140 is inserted into the helicalgroove 410 when the driven-side rotational body 120 is coupled to thedrive-side rotational body 110, the driven-side rotational body 120 isrotated with the pin 141 engaged with the side wall 413 of the helicalgroove 410. Then, while the pin 141 slides on the side wall 413 of thehelical groove 410, the driven-side rotational body 120 moves axiallyfrom the coupled position toward the decoupled position. When the pin141 reaches a finishing end 412 of the helical groove 410, the pin 141is inserted into the annular groove 420 and the driven-side rotationalbody 120 is switched from the coupled position to the decoupledposition. As has been described, the clutch 100 is configured such that,by inserting the pin 141 of the looking member 140 into the groove 400to engage the pin 141 with the side wall 413 of the helical groove 410,the driven-side rotational body 120 is moved to the decoupled positionagainst the urging force of the urging members 135.

When the drive-side rotational body 110 and the driven-side rotationalbody 120 are decoupled from each other, torque transmission from thedrive-side rotational body 110 to the driven-side rotational body 120 isstopped. However, immediately after such decoupling, the driven-siderotational body 120 is continuously rotated by inertial force.Specifically, when the driven-side rotational body 120 is located at thedecoupled position, the pin 141 is inserted in the annular groove 420,which extends over the entire circumference of the driven-siderotational body 120. The driven-side rotational body 120 is thusprohibited from shifting axially. In this state, since torquetransmission from the drive-side rotational body 110 to the driven-siderotational body 120 is stopped, the rotational speed of the driven-siderotational body 120 gradually decreases and such rotation eventuallystops.

The driven-side rotational body 120 is urged toward the coupled positionby the urging force of the urging members 135. Accordingly, to maintainthe decoupled state, the pin 141 of the locking member 140 must bemaintained in a state inserted in the annular groove 420 of thedriven-side rotational body 120. To re-couple the drive-side rotationalbody 110 and the driven-side rotational body 120 to each other, the pin141 is retracted from the annular groove 420 of the groove 400 by meansof the actuator 150. After the pin 141 is retracted in this manner, thelocking member 140 is disengaged from the driven-side rotational body120 and the driven-side rotational body 120 is moved to the coupledposition by the urging force of the urging members 135. As a result, thedrive-side rotational body 110 and the driven-side rotational body 120are returned to the coupled state.

In the groove 400 formed in the outer circumferential surface of thedriven-side rotational body 120, the annular groove 420 is formedcontinuously from the helical groove 410 and extends over the entirecircumference of the outer circumferential surface of the driven-siderotational body 120. The groove 400 of the driven-side rotational body120 thus has a connecting portion at which the annular groove 420 andthe helical groove 410 are connected to each other. Therefore, when thepin 141 is inserted in the annular groove 420 such that the driven-siderotational body 120 is located at the decoupled position but thedriven-side rotational body 120 is continuously rotated by inertialforce, the pin 141 is possibly shifted to the helical groove 410 throughthe connecting portion between the helical groove 410 and the annulargroove 420. To avoid this, the clutch 100 of the first embodimentincludes a restricting portion, which restricts such shifting of the pin141 from the annular groove 420 to the helical groove 410 when the pin141 is inserted in the annular groove 420.

The restricting portion is configured in the manner described below.That is, in the groove 400, as illustrated in FIGS. 2 to 4, the annulargroove 420 has a depth greater than the depth of the helical groove 410.In other words, the bottom surface of the annular groove 420 is locatedradially inward of the bottom surface of the helical groove 410. Theannular groove 420 and the helical groove 410 are thus connectedtogether with a step formed between the annular groove 420 and thehelical groove 410. In the first embodiment, the step, which is the sidewall 423 of the annular groove 420, functions as the restrictingportion.

With reference to FIGS. 2 and 3, the width of the helical groove 410becomes gradually smaller from the starting end 411 to the finishing end412. Therefore, when the inserting position of the pin 141, which hasbeen inserted into the portion of the helical groove 410 in the vicinityof the starting end 411, reaches the finishing end 412 of the helicalgroove 410 as the driven-side rotational body 120 rotates, the pin 141is pressed by the side wall 413 of the helical groove 410 and thusinserted into the annular groove 420, which has a depth greater than thedepth of the helical groove 410.

Further, as illustrated in FIG. 4, the depth of the helical groove 410becomes gradually greater from the starting end 411 to the finishing end412. In other words, the radial position of the bottom surface of thehelical groove 410 approaches the axis of the driven-side rotationalbody 120 gradually from the starting end 411 to the finishing end 412.The depth of the annular groove 420 is small at the starting end 421 ofthe annular groove 420, which corresponds to the finishing end 412 ofthe helical groove 410, relative to the depths of the other portions inthe circumferential direction of the driven-side rotational body 120.The radial distance between the bottom surface of the annular groove 420and the bottom surface of the helical groove 410 is thus small at theportion corresponding to the finishing end 412 of the helical groove 410and the starting end 421 of the annular groove 420, relative to otherportions. That is, at this portion, the step between the helical groove410 and the annular groove 420 is relatively small. This attenuatesimpact applied to the pin 141 when the pin 141 reaches the finishing end412 of the helical groove 410 and is then inserted into the annulargroove 420, which has a depth greater than the depth of the helicalgroove 410, compared to a case in which the size of the step is setuniform in the circumferential direction. Specifically, the step at theaforementioned portion is set to such a size that the aforementionedimpact is attenuated and shifting of the pin 141 from the annular groove420 to the helical groove 410 is restrained.

The structure of the actuator 150 will now be described.

As illustrated in FIG. 4, the actuator 150 of the first embodiment is anelectromagnetic actuator, which is operated through action of a magneticfield generated by energizing a coil 153 accommodated in a first case152.

The first case 152 has a cylindrical shape having a bottom portion and afixed core 154 is fixed to the bottom portion. The coil 153 is arrangedin the first case 152 to surround the fixed core 154. That is, in theactuator 150, the fixed core 154 and the coil 153 configure anelectromagnet. A movable core 155 is movably accommodated in the coil153 of the first case 152 at a position facing the fixed core 154. Thefixed core 154 and the movable core 155 of the first embodiment are bothiron cores.

A cylindrical second case 158 is fixed to a distal end portion (a rightend portion as viewed in FIG. 4) of the first case 152. A permanentmagnet 159 is fixed to an end portion of the second case 158 fixed tothe first case 152 in a manner surrounding the movable core 155. As hasbeen described, the movable core 155 is accommodated in the first case152 such that a proximal end zone (a left end zone as viewed in FIG. 4)of the movable core 155 faces the fixed core 154. A distal end zone (aright end zone as viewed in the drawing) projects outward from thesecond case 158.

A ring member 160 is attached to the portion of the movable core 155that is accommodated in the second case 158. A coil spring 161, whichhas an end secured to the second case 158 and an opposite end secured tothe ring member 160, is accommodated in the second case 158 in acompressed state.

The coil spring 161 urges the movable core 155 in the direction in whichthe movable core 155 projects from the second case 158 (rightward asviewed in FIG. 4). The portion of the movable core 155 that projectsfrom the second case 158 is coupled to the locking member 140 through afixing pin 162.

The locking member 140 is pivotally coupled to the movable core 155 atthe proximal end of the locking member 140 and pivotally supported by apivot shaft 156. This allows the locking member 140 to pivot about thepivot shaft 156, which is a support point of pivot, when the movablecore 155 moves. As a result, as represented by the solid lines in FIG.4, as the extent of projection of the movable core 155 from the secondcase 158 is increased by the urging force of the coil spring 161, thepin 141 of the locking member 140 is inserted sequentially into thehelical groove 410 and the annular groove 420 of the driven-siderotational body 120.

If the coil 153 is energized in this state, a magnetic field isgenerated through such energization to magnetize the fixed core 154 andthe movable core 155. The movable core 155 is thus attracted to thefixed core 154 against the urging force of the coil spring 161. Thedirection of the magnetic field generated by the coil 153 at this stagematches with the direction of the magnetic field generated by thepermanent magnet 159.

As the movable core 155 is attracted and moved toward the fixed core 154(leftward as viewed in FIG. 4), the locking member 140 is pivotedclockwise as viewed in FIG. 4 to retract the distal end of the lockingmember 140 from the groove 400. That is, the actuator 150 retracts thelocking member 140 from the groove 400 by attracting the movable core155 using magnetic force produced through energization of the coil 153.

After the movable core 155 is attracted and moved to a contact positionat which the movable core 155 contacts the fixed core 154 (the positionrepresented by the long dashed double-short dashed lines in FIG. 4), themovable core 155 is held in contact with the fixed core 154 by themagnetic force of the permanent magnet 159 even if the energization isstopped afterwards.

In contrast, if the coil 153 is energized by an electric current flowingin the opposite direction to the direction of the electric current forattracting the movable core 155 when the movable core 155 is arranged atthe contact position represented by the long dashed double-short dashedlines in FIG. 4, a magnetic field is generated in the opposite directionto the direction of the magnetic field of the permanent magnet 159. Thisattenuates the attracting force of the permanent magnet 159, and themovable core 155 is separated from the fixed core 154 by the urgingforce of the coil spring 161. The movable core 155 then moves to theprojected position represented by the solid lines in FIG. 4. As themovable core 155 is moved from the contact position to the projectedposition, the locking member 140 is pivoted counterclockwise as viewedin FIG. 4 and the pin 141 of the locking member 140 is inserted into thegroove 400.

When the movable core 155 is located at the projected position at whichthe movable core 155 is separated from the fixed core 154, the urgingforce of the coil spring 161 exceeds the attracting force of thepermanent magnet 159. As a result, if the coil 153 is energized toseparate the movable core 155 from the fixed core 154, the movable core155 is held at the projected position even after such energization isstopped afterward.

That is, the actuator 150 of the first embodiment is a self-holding typesolenoid, which switches the engagement state of the clutch 100 byapplying direct electric currents in different directions and thusmoving the movable core 155 and does not need the energization tomaintain the clutch 100 in either the engaged state or the disengagedstate.

Operation of the clutch 100 according to the present embodiment will nowbe described.

As represented by the long dashed double-short dashed lines in FIG. 4,when the movable core 155 of the actuator 150 is arranged at the contactposition, the pin 141 of the locking member 140 is located in theexterior of the groove 400. At this stage, the driven-side rotationalbody 120 is held at the coupled position by the urging force of theurging members 135 such that the clutch 100 is in the engaged state.That is, the clutch 100 transmits rotation of the drive-side rotationalbody 110 to the output shaft 210.

If, in this state, the coil 153 of the actuator 150 is energized togenerate a magnetic field in the opposite direction to the direction ofthe magnetic field of the permanent magnet 159, the movable core 155 ismoved from the contact position to the projected position represented bythe solid lines in FIG. 4 by the urging force of the coil spring 161.This pivots the locking member 140 counterclockwise as viewed in FIG. 4,thus inserting the pin 141 of the locking member 140 into the portion ofthe helical groove 410 of the groove 400 of the driven-side rotationalbody in the vicinity of the starting end 411. The driven-side rotationalbody 120 is thus stopped and held in the state illustrated in FIG. 3.

When the driven-side rotational body 120 is rotated together with thedrive-side rotational body 110 with the pin 141 locking the driven-siderotational body 120 and the pin 141 is moved relatively in the helicalgroove 410, the driven-side rotational body 120 is moved from thecoupled position to the decoupled position and thus switched from thestate illustrated in FIG. 3 to the state illustrated in FIG. 2. In thismanner, the pin 141 is switched to a state inserted in the annulargroove 420 and the driven-side rotational body 120 reaches the decoupledposition. This stops transmission of rotation of the drive-siderotational body 110 to the driven-side rotational body 120, thusdisengaging the clutch 100.

Immediately after the driven-side rotational body 120 and the drive-siderotational body 110 are disengaged from each other, the driven-siderotational body 120 is continuously rotated by inertial force whilereceiving action of friction force produced between the driven-siderotational body 120 and the pin 141, which is inserted in the annulargroove 420 as shown in FIG. 2. When the pin 141 is inserted in theannular groove 420 and the driven-side rotational body 120 is rotating,the pin 141 is engaged with the step in the boundary between the helicalgroove 410 and the annular groove 420, which is the side wall 423 of theannular groove 420. Therefore, unless the pin 141 is shifted to beretracted from the annular groove 420 and thus move past the step, thepin 141 cannot be shifted into the helical groove 410, so that shiftingof the pin 141 from the annular groove 420 into the helical groove 410is restricted. In this manner, the driven-side rotational body 120 isrotated with the pin 141 of the locking member 140 inserted in theannular groove 420 of the driven-side rotational body 120. Therotational speed of the driven-side rotational body 120 then decreasesgradually until the driven-side rotational body 120 eventually stopsrotating.

To switch the clutch 100 from the disengaged state to the engaged state,the coil 153 of the actuator 150 is energized to generate a magneticfield in the same direction as the direction of the magnetic field ofthe permanent magnet 159. The movable core 155 is thus attracted towardthe fixed core 154 by magnetic force produced by energization and movedfrom the projected position represented by the solid lines in FIG. 4 tothe contact position represented by the long dashed double-short dashedlines in the drawing. This pivots the locking member 140 clockwise asviewed in FIG. 4, thus fully retracting the pin 141 of the lockingmember 140 from the groove 400.

After having been released from the locking member 140, the driven-siderotational body 120 is moved to the coupled position by the urging forceof the urging members 135. The driven-side rotational body 120 and thedrive-side rotational body 110 thus become coupled to each other,switching the clutch 100 to the engaged state.

The above described embodiment provides the following advantages.

(1) In the first embodiment, when the pin 141 of the locking member 140is inserted in the helical portion of the driven-side rotational body120, the driven-side rotational body 120 is rotated with the pin 141engaged with the side wall 413 of the helical portion. This moves thedriven-side rotational body 120 from the coupled position to thedecoupled position against the urging force of the urging members 135.In this manner, the force needed to disengage the clutch 100 is obtainedfrom the rotational force of the driven-side rotational body 120. As aresult, the drive-side rotational body 110 and the driven-siderotational body 120 are disengaged from each other by small force.

(2) In the first embodiment, when the pin 141 is inserted in the annulargroove 420, the pin 141 is engaged with the side wall 423 at the step inthe boundary between the helical groove 410 and the annular groove 420.Therefore, unless the pin 141 is shifted to be retracted from theannular groove 420 and moves past the step, the pin 141 cannot beshifted to the helical groove 410. That is, when the pin 141 is insertedin the annular groove 420, the side wall 423 at the step in the boundarybetween the helical groove 410 and the annular groove 420 functions as arestricting portion. This restricts shifting of the pin 141 from theannular groove 420 to the helical groove 410, thus restraining shiftingof the driven-side rotational body 120 to the coupled position despitethe fact that the pin 141 is maintained in the groove 400.

(3) In the first embodiment, the depth of the annular groove 420 issmall in the vicinity of the starting end 421 relative to the depths ofthe other portions in the circumferential direction of the driven-siderotational body 120. The depth of the helical groove 410 becomesgradually greater from the starting end 411 to the finishing end 412.The step between the finishing end 412 of the helical groove 410 and thestarting end 421 of the annular groove 420 is small-sized relative tosteps in other portions. This attenuates impact applied to the pin 141when the pin 141 is moved from the helical groove 410 and inserted intothe annular groove 420, the depth of which is greater than the depth ofthe helical groove 410, compared to a case in which the step between theannular groove 420 and the helical groove 410 is set to a uniform sizein the circumferential direction of the driven-side rotational body 120.

Second Embodiment

A clutch according to a second embodiment will now be described withreference to FIGS. 5 to 7.

As illustrated in FIG. 5, a clutch 500 of the second embodiment isdifferent from the first embodiment in terms of the configuration of agroove 520 formed in an outer circumferential surface of a smalldiameter portion 511 of a driven-side rotational body 510 and theconfiguration of a pin 560 of a locking member 550. The remainder of theconfiguration is the same as those of the first embodiment. Thus, likeor the same reference numerals are given to those components that arelike or the same as the corresponding components of the first embodimentand detailed explanations are omitted.

In the second embodiment, the groove 520 of the driven-side rotationalbody 510 has a helical groove 530 inclined with respect to the axialdirection and an annular groove 540, which is formed continuously fromthe helical groove 530 and extends over the entire circumference of anouter circumferential surface of the driven-side rotational body 510 andperpendicularly to the axial direction.

With reference to FIGS. 5 to 7, the annular groove 540 has a connectingportion 541, which has a depth equal to the depth of the helical groove530 and is connected to the helical groove 530, and a non-connectingportion 542, which is disconnected from the helical groove 530. In FIGS.5 to 7, the boundary between the connecting portion 541 of the annulargroove 540 and the helical groove 530 is represented by the long dasheddouble-short dashed line. The long dashed double-short dashed linerepresenting the boundary coincides with the extended line of a sidewall 544 of the non-connecting portion 542 of the annular groove 540.

A protrusion 543, which protrudes from the bottom surface of the annulargroove 540 and extends in the extending direction of the annular groove540, is formed in the annular groove 540. The protrusion 543 is formedover the entire length of the connecting portion 541. The opposite endsof the protrusion 543 are arranged in the non-connecting portion 542.The protrusion 543 of the annular groove 540 has a uniform width and isinclined with respect to the axial direction of the driven-siderotational body 510 by the inclination angle equal to the inclinationangle of a side wall 531 of the helical groove 530. As a result, withreference to FIG. 7, the distance from the side wall 531 of the helicalgroove 530 to the protrusion 543 is a uniform distance d1 in thecircumferential direction of the driven-side rotational body 510.

As shown in FIGS. 5 to 7, a recess 561, into which the protrusion 543can proceed, is formed at the distal end of the pin 560 of the lockingmember 550. In FIG. 7, states of relative movement of the pin 560 of thelocking member 550 in the groove 520 when the driven-side rotationalbody 510 is in a rotating state are illustrated by way of pins 560represented by the long dashed double-short dashed lines. In the secondembodiment, the protrusion 543, which projects from the bottom surfaceof the annular groove 540, and the recess 561 of the pin 560 configure arestricting portion.

Referring to FIG. 7, the width d2 of the pin 560 of the locking member550 is slightly smaller than the distance d1 from the side wall 531 ofthe helical groove 530 to the protrusion 543. The distance d3 from astarting end of the protrusion 543, which is the end portion of theprotrusion 543 that the pin 560 reaches first when the driven-siderotational body 510 is rotated, to the side wall 544 of the annulargroove 540 is substantially equal to but slightly greater than thelength d4 from the side surface of the pin 560 to the recess 561. Thewidth d5 of the recess 561 is greater than the width d6 of theprotrusion 543.

Operation of the present embodiment will now be described.

As illustrated in FIG. 6, when the driven-side rotational body 510 is ina state coupled to the drive-side rotational body 110, the actuator 150is operated to insert the pin 560 of the locking member 550 into astarting end 532 of the helical groove 530 of the groove 520. Thisengages the pin 560 with the side wall 531 of the helical groove 530 tolocks the driven-side rotational body 120 against the urging force ofthe urging members 135. Then, as the driven-side rotational body 510 isrotated, the pin 560 is moved relatively in the groove 520 in acircumferential direction while being engaged with the side wall 531 ofthe helical groove 530. The width d2 of the pin 560 is slightly smallerthan the distance d1 from the side wall 531 of the helical groove 530 tothe protrusion 543. This restrains interference of the protrusion 543with movement of the pin 560 when the pin 560 is engaged with the sidewall 531 of the helical groove 530 and moved relatively in the groove520, thus allowing relative movement of the pin 560 in the helicalgroove 530. The pin 560 thus reaches the annular groove 540 and is thenmoved relatively in the annular groove 540 of the groove 520 as thedriven-side rotational body 510 is rotated. The driven-side rotationalbody 510 is rotated by inertial force at the decoupled position.

As has been described, the distance d3 from the starting end of theprotrusion 543 to the side wall 544 of the annular groove 540 issubstantially equal to but slightly greater than the length d4 from theside wall of the pin 560 to the recess 561. The width d5 of the recess561 is greater than the width d6 of the protrusion 543. Therefore, whenthe driven-side rotational body 510 is rotated and the pin 560 is movedrelatively in the annular groove 540 to reach the starting end of theprotrusion 543, which is arranged in the annular groove 540, theprotrusion 543 proceeds into the recess 561 and becomes engaged with therecess 561. The protrusion 543 extends in the extending direction of theannular groove 540 and is formed over the entire length of theconnecting portion 541. As a result, even if the driven-side rotationalbody 510 is rotated by inertial force and the pin 560 is moved to theconnecting portion 541 of the annular groove 540 such that the pin 560and the side surface of the groove 520, which is the side wall 544 ofthe annular groove 540 corresponding to the non-connecting portion 542,become separate from each other, the pin 560 is engaged with theprotrusion 543 and thus held in the annular groove 540.

To switch the clutch 500 from the disengaged state to the engaged state,the actuator 150 is operated to retract the pin 560 of the lockingmember 550 from the annular groove 540 of the groove 520. This alsocauses disengagement between the recess 561 of the pin 560 and theprotrusion 543 of the annular groove 540. By retracting the pin 560 ofthe locking member 550 from the groove 520 in this manner, thedriven-side rotational body 510 is moved to the coupled position by theurging force of the urging members 135. The driven-side rotational body510 and the drive-side rotational body 110 thus become coupled to eachother, switching the clutch 500 to the engaged state.

The second embodiment achieves the following advantage (4) as well as anadvantage equivalent to the advantage (1) of the first embodiment.

(4) In the second embodiment, shifting of the pin 560 from the annulargroove 540 to the helical groove 530 is restricted unless the pin 560 isshifted to be retracted from the annular groove 540 and the recess 561of the pin 560 and the protrusion 543 of the annular groove 540 aredisengaged from each other. That is, when the pin 560 is inserted in theannular groove 540, the recess 561 of the pin 560 and the protrusion 543of the annular groove 540 function as a restricting portion. Therefore,since shifting of the pin 560 from the annular groove 540 to the helicalgroove 530 is restricted, it is possible to restrain shifting of thedriven-side rotational body 510 to the coupled position despite the factthat the pin 560 is maintained in the groove 520.

Third Embodiment

A clutch according to a third embodiment will now be described withreference to FIGS. 8 to 10.

As illustrated in FIG. 8, a clutch 600 of the third embodiment isdifferent from the illustrated embodiments in terms of the configurationof a groove 620 formed in an outer circumferential surface of a smalldiameter portion 611 of a driven-side rotational body 610 and theconfiguration of a pin 660 of a locking member 650. The remainder of theconfiguration is the same as those of the first embodiment. Thus, likeor the same reference numerals are given to those components that arelike or the same as the corresponding components of the first embodimentand detailed explanations are omitted.

In the third embodiment, the groove 620 of the driven-side rotationalbody 610 has a helical groove 630 inclined with respect to the axialdirection and an annular groove 640, which is formed continuously fromthe helical groove 630 and extends over the entire circumference of anouter circumferential surface of the driven-side rotational body 610 andperpendicularly to the axial direction.

As illustrated in FIGS. 8 to 10, the annular groove 640 has a connectingportion 641, which has a depth equal to the depth of the helical groove630 and is connected directly to the helical groove 630, and anon-connecting portion 642, which is not connected directly to thehelical groove 630. In FIGS. 8 to 10, the boundary between theconnecting portion 641 of the annular groove 640 and the helical groove630 is represented by the long dashed double-short dashed line. The longdashed double-short dashed line representing the boundary coincides withthe extended line of a side wall 644 of the non-connecting portion 642of the annular groove 640.

A recessed groove 643, which extends in the extending direction of theannular groove 640, is formed in the annular groove 640. Specifically,the recessed groove 643 extends in a direction perpendicular to theaxial direction of the driven-side rotational body 610. Also, therecessed groove 643 extends over the entire length of the annular groove640. That is, the recessed groove 643 is formed over the entirecircumference of the outer circumferential surface of the driven-siderotational body 610.

With reference to FIGS. 8 to 10, a projection 661, which can be insertedinto the recessed groove 643, projects from the distal end of the pin660 of the locking member 650. In FIG. 10, states of relative movementof the pin 660 of the locking member 650 in the groove 620 when thedriven-side rotational body 610 is in a rotating state are illustratedby pins 660 represented by the long dashed double-short dashed lines. Inthe third embodiment, the recessed groove 643, which is formed in thebottom surface of the annular groove 640, and the projection 661 of thepin 660 configure a restricting portion.

Referring to FIG. 10, the length d1 from the side surface of the pin 660of the locking member 650 to the projection 661 is substantially equalto but slightly greater than the distance d2 from the side wall 644 ofthe annular groove 640 to the recessed groove 643. The width d3 of theprojection 661 of the pin 660 is smaller than the width d4 of therecessed groove 643 of the annular groove 640.

Operation of the present embodiment will now be described.

As illustrated in FIG. 9, when the driven-side rotational body 610 is ina state coupled to the drive-side rotational body 110, the actuator 150is operated to insert the pin 660 of the locking member 650 into astarting end 632 of the helical groove 630 of the groove 620. Thisengages the pin 660 with a side wall 631 of the helical groove 630 tolock the driven-side rotational body 120 against the urging force of theurging members 135. Then, as the driven-side rotational body 610 isrotated, the pin 660 is moved relatively in the groove 620 in acircumferential direction while being engaged with the side wall 631 ofthe helical groove 630. The pin 660 thus reaches the annular groove 640and the driven-side rotational body 610 is moved to a decoupled positionand rotated by inertial force. As a result, with reference to FIG. 8,the pin 660 is switched to a state moving relatively in the annulargroove 640.

As has been described, the length d1 from the side surface of the pin660 of the locking member 650 to the projection 661 is substantiallyequal to but slightly greater than the distance d2 from the side wall644 of the annular groove 640 to the recessed groove 643. The width d3of the projection 661 of the pin 660 is smaller than the width d4 of therecessed groove 643 of the annular groove 640. Therefore, when thedriven-side rotational body 610 is rotated and the pin 660 is movedrelatively in the annular groove 640, the projection 661 of the pin 660proceeds into the recessed groove 643, which is formed in the annulargroove 640, and becomes engaged with the recessed groove 643. Therecessed groove 643 extends in the extending direction of the annulargroove 640 and is formed over the entire length of the annular groove640. As a result, even if the driven-side rotational body 610 is rotatedby inertial force and the pin 660 is moved to the connecting portion 641of the annular groove 640 such that the pin 660 and the side surface ofthe groove 620, which is the side wall 644 of the annular groove 640corresponding to the non-connecting portion 642, become separate fromeach other, the projection 661 of the pin 660 is engaged with therecessed groove 643. The pin 660 is thus maintained in the annulargroove 640.

To switch the clutch 600 from the disengaged state to the engaged state,the actuator 150 is operated to retract the pin 660 of the lockingmember 650 from the annular groove 640 of the groove 620. This alsocauses retraction of the projection 661 of the pin 660 from the recessedgroove 643 of the annular groove 640, thus disengaging the projection661 of the pin 660 and the recessed groove 643 of the annular groove 640from each other. The driven-side rotational body 510 is then moved tothe coupled position by the urging force of the urging members 135. As aresult, the driven-side rotational body 510 and the drive-siderotational body 110 become coupled to each other, thus switching theclutch 500 to the engaged state.

The third embodiment achieves the following advantage (5) as well as anadvantage equivalent to the advantage (1) of the first embodiment.

(5) In the third embodiment, shifting of the pin 660 from the annulargroove 640 to the helical groove 630 is restricted unless the pin 660 isshifted to be retracted from the annular groove 640 and the recessedgroove 643 and the projection 661 of the pin 660 are disengaged fromeach other. That is, when the pin 660 is inserted in the annular groove640, the recessed groove 643 and the projection 661 of the pin 660function as a restricting portion. As a result, since shifting of thepin 660 from the annular groove 640 to the helical groove 630 isrestricted, it is possible to restrain shifting of the driven-siderotational body 610 to the coupled position despite the fact that thepin 660 is maintained in the recessed groove 643.

Modification of Third Embodiment

As illustrated in FIG. 11, the present modification is different fromthe third embodiment in terms of the configuration of a helical groove680 of a groove 670 of the driven-side rotational body. Specifically, inthe modification, a recessed groove 681, which extends in the extendingdirection of the helical groove 680, is formed also in the helicalgroove 680. The recessed groove 681 of the helical groove 680 isconnected to the recessed groove 643 of the annular groove 640.

If the actuator 150 is operated to insert the pin 660 of the lockingmember 650 into the helical groove 630 of the groove 620 when thedriven-side rotational body 610 is in a state coupled to the drive-siderotational body 110, the pin 660 becomes engaged with the side wall 631of the helical groove 630. Also, the projection 661 of the pin 660proceeds into the recessed groove 681 of the helical groove 680 andbecomes engaged with the recessed groove 681. Then, when the driven-siderotational body is rotated and the pin 660 is moved relatively in thehelical groove 630, engagement between the projection 661 and therecessed groove 681 is maintained. In this state, where such engagementis maintained, the pin 660 reaches the annular groove 640. Therefore,after the pin reaches the annular groove 640, the projection 661proceeds into the recessed groove 643 of the annular groove 640 throughthe connecting portion between the recessed groove 681 of the helicalgroove 680 and the recessed groove 643 of the annular groove 640. Thatis, the recessed groove 681 of the helical groove 680 guides theprojection 661 of the pin 660 into the recessed groove 643 of theannular groove 640.

Also in this embodiment, the recessed groove 643 extends in theextending direction of the annular groove 640 and is formed over theentire length of the annular groove 640. As a result, even if thedriven-side rotational body 610 is rotated by inertial force and the pin660 is moved to the connecting portion 641 of the annular groove 640such that the pin 660 and the side surface of the groove 620 becomeseparate from each other, the projection 661 of the pin 660 is engagedwith the recessed groove 643. The pin 660 is thus maintained in theannular groove 640.

The remainder of the configuration, the operation, and the advantages ofthe present modification are the same as those of the third embodiment.

Fourth Embodiment

A clutch according to a fourth embodiment will now be described withreference to FIG. 12.

As illustrated in FIG. 12, a clutch 700 of the fourth embodiment isdifferent from the illustrated embodiments in terms of the configurationof a driven-side rotational body 710 and the configuration of a lockingmember 750. The remainder of the configuration is the same as those ofthe first embodiment. Thus, like or the same reference numerals aregiven to those components that are like or the same as the correspondingcomponents of the first embodiment and detailed explanations areomitted. Position change of each ball 130 in the corresponding ballaccommodating groove 127 caused by axial shifting of the driven-siderotational body 710 and switching between the engaged state and thedisengaged state caused by such position change happen in the samemanners as the first embodiment. Accordingly, illustration of the balls130 and the ball accommodating grooves 127 are omitted in FIG. 12.

As illustrated in FIG. 12, a groove 720 of a small diameter portion 711of the driven-side rotational body 710 includes a helical groove 730inclined with respect to the axial direction and an annular groove 740,which is formed continuously from the helical groove 730 and extendsover the entire circumference of an outer circumferential surface of thedriven-side rotational body 710 and perpendicularly to the axialdirection. The annular groove 740 of the groove 720 has a depth equal tothe depth of the helical groove 730. In FIG. 12, the boundary between aconnecting portion of the annular groove 740, which is connecteddirectly to the helical groove 730, and the helical groove 730 isrepresented by the long dashed double-short dashed line.

A flange 770 projects from the outer circumferential surface of thedriven-side rotational body 710 and extends over the entirecircumference of the outer circumferential surface of the driven-siderotational body 710. Specifically, the flange 770 is arranged on anouter circumferential surface of the small diameter portion 711 of thedriven-side rotational body 710. That is, the flange 770 is formed at aright side as viewed in FIG. 12A with respect to a groove 720 in theouter circumferential surface of the driven-side rotational body. Theflange 770 extends perpendicular to the axial direction of thedriven-side rotational body 710 and parallel to the annular groove 740.

The locking member 750 includes a pin 760, which is inserted into thegroove 720 of the driven-side rotational body 710, and a one-way lockingportion 780, which selectively proceeds and retreats with respect to thedriven-side rotational body 710 as the pin 760 is inserted into orretracted from the groove 720. In the fourth embodiment, the one-waylocking portion 780 and the flange 770 of the driven-side rotationalbody 710 configure a restricting portion.

The one-way locking portion 780 includes an engagement member 781 and anelastic member 785, which urges the engagement member 781 toward thedriven-side rotational body 710. The elastic member 785 is configuredby, for example, a coil spring. The one-way locking portion 780 islocated at the same side with respect to the pin 760 as the side atwhich the flange 770 is arranged with respect to the groove 720 (theright side as viewed in FIG. 12A).

The right surface of the flange 770 as viewed in FIG. 12A is referred toas a first surface 771 and the left surface of the flange 770 as viewedin the drawing is referred to as a second surface 772. The right surfaceof the engagement member 781 as viewed in FIG. 12A is referred to as afirst surface 782 and the left surface of the engagement member 781 asviewed in the drawing is referred to as a second surface 783. The rightsurface of the pin 760 as viewed in FIG. 12A is referred to as a firstsurface 761. In this case, the distances between the respective surfacesand the shapes of the surfaces 782, 783 of the engagement member 781 aredefined as follows.

As illustrated in FIG. 12A, in the locking member 750, the distance d1from the first surface 761 of the pin 760 to the second surface 783 ofthe engagement member 781 is substantially equal to but slightly greaterthan the distance d2 from a side wall 732 at a starting end 731 of thehelical groove 730 to the first surface 771 of the flange 770. Thedistance d3 from the first surface 761 of the pin 760 of the lockingmember 750 to the first surface 782 of the engagement member 781 issubstantially equal to but slightly smaller than the distance d4 from aside wall 741 of the annular groove 740 (the position represented by thelong dashed double-short dashed line in the connecting portion of theannular groove 740) to the second surface 772 of the flange 770. In theengagement member 781, the distal end of the first surface 782 is acorner and the distal end of the second surface 783 is a chamfered roundsurface. That is, the second surface 783 is inclined such that the firstsurface 782 approaches the first surface 782 in a distal direction. Inother words, the distal end of the engagement member 781 is inclined andbecomes gradually smaller in size.

Accordingly, when the driven-side rotational body 710 is in a coupledstate and the pin 760 is inserted in the starting end 731 of the helicalgroove 730 of the groove 720 as illustrated in FIG. 12B, the secondsurface 783 of the engagement member 781 is in contact with the firstsurface 771 of the flange 770. The second surface 783 of the engagementmember 781, which contacts the flange 770 at this stage, has theinclined distal end as has been described. Also, referring to FIG. 12D,when the pin 760 is inserted in the annular groove 740 of the groove720, the engagement member 781 is in contact with the second surface 772of the flange 770. The distal end of the first surface 782 of theengagement member 781, which contacts the flange 770 at this stage, isthe corner as has been described.

Operation of the present embodiment will now be described.

Referring to FIG. 12A, the driven-side rotational body 710 is located ata coupled position and the driven-side rotational body 710 is in a statecoupled to the drive-side rotational body 110. In this state, byoperating the actuator 150 to insert the pin 760 of the locking member750 into the helical groove 730 of the groove 720, the state illustratedin. FIG. 12B is brought about. In this manner, the pin 760 is engagedwith a side wall 732 of the helical groove 730, thus locking thedriven-side rotational body 120 against the urging force of the urgingmembers 135. Then, as the driven-side rotational body 710 is rotated,the pin 760 is moved relatively in the groove 720 in a circumferentialdirection while being engaged with the side wall 732 of the helicalgroove 730. The driven-side rotational body 710 is thus shifted from thecoupled position to a decoupled position.

As the driven-side rotational body 710 is shifted to the decoupledposition, the position of the pin 760 in the groove 720 is shiftedrelatively in a direction from the helical groove 730 toward the annulargroove 740. Correspondingly, the engagement member 781, which is fixedto the locking member 750 together with the pin 760, is shifted relativeto the driven-side rotational body 710. As illustrated in FIG. 123, whenthe pin 760 is inserted in the starting end 731 of the helical groove730 of the groove 720, the engagement member 781 faces the first surface771 of the flange 770. The second surface 783 of the engagement member781, which faces the flange 770, has the inclined distal end. That is,the surface by which the engagement member 781 contacts the flange 770when the driven-side rotational body 710 is shifted from the coupledposition to the decoupled position is inclined. Therefore, when thedriven-side rotational body 710 is moved from the coupled position tothe decoupled position, the flange 770 and the engagement member 781contact each other, as illustrated in FIG. 12C, to cause the force forpressing the engagement member 781 back against the urging force of theelastic member 785 such that the engagement member 781 moves past theflange 770. In this manner, when the pin 760 is inserted in the helicalgroove 730 of the groove 720, movement of the driven-side rotationalbody 710 from the coupled position to the decoupled position ispermitted despite the fact that the engagement member 781 is in contactwith the flange 770.

Then, as illustrated in FIG. 12D, when the driven-side rotational body710 is rotated by inertial force at the decoupled position and the pin760 is moved relatively in the annular groove 740, the engagement member781 faces the first surface 771 of the flange 770. As has beendescribed, the first surface 782 of the engagement member 781 contactsthe flange 770 in this state and the distal end of the first surface 782is the corner. Therefore, when the pin 760 is moved relatively in theannular groove 740 of the groove 720, the engagement member 781 isprevented from being pressed back by the flange 770 against the urgingforce of the elastic member 785, and engagement between the engagementmember 781 and the flange 770 is thus maintained. In this manner,movement of the driven-side rotational body 710 from the decoupledposition to the coupled position is restricted. That is, even when thedriven-side rotational body 710 is arranged at the decoupled positionand rotated by inertial force and, in this state, the pin 760 is movedto the connecting portion of the annular groove 740 to separate the pin760 from the side surface of the groove 720 (the side wall 741 of theannular groove 740), the one-way locking portion 780 restricts shiftingof the driven-side rotational body 710. The pin 760 is thus held in theannular groove 740.

To switch the clutch 700 from the disengaged state to the engaged state,the actuator 150 is operated to retract the pin 760 of the lockingmember 750 from the annular groove 740 of the groove 720. This alsocauses disengagement between the engagement member 781 and the flange770. The driven-side rotational body 710 is thus moved to the coupledposition by the urging force of the urging members 135. As a result, thedriven-side rotational body 710 and the drive-side rotational body 110become coupled to each other, thus switching the clutch 700 to theengaged state.

The fourth embodiment achieves the following advantage (6) as well as anadvantage equivalent to the advantage (1) of the first embodiment.

(6) Unless the pin 760 is shifted to be retracted from the annulargroove 740 to disengage the flange 770 and the one-way locking portion780 from each other, the pin 760 is not shifted from the annular groove740 to the helical groove 730. That is, the flange 770 and the one-waylocking portion 780 function as a restricting portion. This restrictsshifting of the pin 760 from the annular groove 740 to the helicalgroove 730 when the pin 760 is inserted in the annular groove 740. As aresult, it is possible to restrain shifting of the driven-siderotational body 710 to the coupled position despite the fact that thepin 760 is maintained in the groove 720.

Fifth Embodiment

A clutch according to a fifth embodiment will now be described.

As illustrated in FIG. 13, a clutch 800 of the fifth embodiment isdifferent from the fourth embodiment in terms of the configuration ofthe locking member 750. The remainder of the configuration is the sameas those of the first embodiment. Thus, like or the same referencenumerals are given to those components that are like or the same as thecorresponding components of the first embodiment and detailedexplanations are omitted. The fifth embodiment is the same as the firstembodiment in terms of position change of each ball 130 in thecorresponding ball accommodating groove 127 caused by axial shifting ofthe driven-side rotational body 710 and switching between the engagedstate and the disengaged state caused by such position change.Accordingly, illustration of the balls 130 and the ball accommodatinggrooves 127 is omitted also in FIG. 13.

With reference to FIG. 13, the driven-side rotational body 710 of thefifth embodiment is configured identically with the driven-siderotational body 710 of the fourth embodiment. The flange 770 is formedin the driven-side rotational body 710.

A locking member 850 includes a pin 860, which is inserted into thegroove 720 of the driven-side rotational body 710, and a one-way lockingportion 880, which selectively proceeds and retreats with respect to thedriven-side rotational body 710 as the pin 860 is inserted into orretracted from the groove 720. In the fifth embodiment, the one-waylocking portion 880 and the flange 770 of the driven-side rotationalbody 710 configure a restricting portion.

The one-way locking portion 880 includes an engagement member 881, apivot shaft 885 through which the engagement member 881 is pivotallysupported by the locking member 850, and a restricting member 888, whichrestricts pivot of the engagement member 881 in a certain direction (aleftward direction in FIG. 13A). As illustrated in FIG. 13A, a state inwhich the distal end of the engagement member 881 projects toward thedriven-side rotational body 710 is defined as a reference position ofthe engagement member 881. The restricting member 888 restricts tiltingof the engagement member 881 in a specific direction from the referenceposition and permits tilting of the engagement member 881 in anotherdirection (a rightward direction in FIG. 13A) from the referenceposition.

The right surface of the flange 770 as viewed in FIG. 13A is referred toas the first surface 771 and the left surface of the flange 770 asviewed in the drawing is referred to as the second surface 772. Theright surface of the engagement member 881 as viewed in FIG. 13A and theleft surface of the engagement member 881 as viewed in the drawing whenthe engagement member 881 is arranged at the reference position arereferred to as a first surface 882 and a second surface 883,respectively. The right surface of the pin 860 as viewed in FIG. 13A isreferred to as a first surface 861.

In this case, the distances between the respective surfaces are definedas follows.

As illustrated in FIG. 13A, in the locking member 850, the distance d1from the first surface 861 of the pin 860 to the second surface 883 ofthe engagement member 881 is substantially equal to but slightly greaterthan the distance d2 from the side wall 732 of the helical groove 730 atthe starting end 731 to the first surface 771 of the flange 770. Thedistance d3 from the first surface 861 of the pin 860 of the lockingmember 850 to the first surface 882 of the engagement member 881 issubstantially equal to but slightly smaller than the length d4 from theside wall 741 of the annular groove 740 (the position represented by thelong dashed double-short dashed line corresponding to the boundaryposition between the annular groove 740 and the helical groove 730 inthe connecting portion of the annular groove 740) to the second surface772 of the flange 770.

Accordingly, when the driven-side rotational body 710 is in a coupledstate and the pin 860 is inserted in the starting end 731 of the helicalgroove 730 of the groove 720 as illustrated in FIG. 13B, the secondsurface 883 of the engagement member 881 is in contact with the firstsurface 771 of the flange 770. Also, as illustrated in FIG. 13D, whenthe pin 860 is arranged in the annular groove 740 of the groove 720, theengagement member 881 is in contact with the second surface 772 of theflange 770.

Operation of the present embodiment will now be described.

Referring to FIG. 13A, the driven-side rotational body 710 is located ata coupled position and the driven-side rotational body 710 is in a statecoupled to the drive-side rotational body 110. In this state, byoperating the actuator 150 to insert the pin 860 of the locking member850 into the starting end 731 of the helical groove 730 of the groove720, the state illustrated in FIG. 13B is brought about. In this manner,the pin 860 is engaged with the side wall 732 of the helical groove 730,thus locking the driven-side rotational body 120 against the urgingforce of the urging members 135. Then, as the driven-side rotationalbody 710 is rotated, the pin 860 is moved relatively in the groove 720in a circumferential direction while being engaged with the side wall732 of the helical groove 730. The driven-side rotational body 710 isthus shifted from the coupled position to a decoupled position.

As the driven-side rotational body 710 is shifted to the decoupledposition, the position of the pin 860 in the groove 720 is shiftedrelatively in a direction from the helical groove 730 toward the annulargroove 740. Correspondingly, the engagement member 881, which is fixedto the locking member 850 together with the pin 860, is shifted relativeto the driven-side rotational body 710. As illustrated in FIG. 13B, whenthe pin 860 is inserted in the starting end 731 of the helical groove730, the engagement member 881 is in contact with the first surface 771of the flange 770. The engagement member 881 is permitted to tilt in thecertain direction (the rightward direction as viewed in FIGS. 13) fromthe reference position, at which the engagement member 881 contacts theflange 770. Therefore, when the driven-side rotational body 710 is movedfrom the coupled position to the decoupled position, the engagementmember 881 contacts the flange 770 and tilts, thus moves past the flange770, as illustrated in FIG. 13C. In this manner, when the pin 860 isinserted in the starting end 731 of the helical groove 730, movement ofthe driven-side rotational body 710 from the coupled position to thedecoupled position is permitted despite the fact that the engagementmember 881 is in contact with the flange 770.

Then, as illustrated in FIG. 13D, when the driven-side rotational body710 is rotated by inertial force at the decoupled position and the pin860 is moved relatively in the annular groove 740, the engagement member881 faces the second surface 772 of the flange 770 and the first surface882 of the engagement member 881 contacts and becomes engaged with thesecond surface 772 of the flange 770. When the pin 860 is movedrelatively in the annular groove 740 of the groove 720, tilting of theengagement member 881 in the certain direction (the leftward directionas viewed in FIG. 13D) is restricted by the restricting member 888. Theengagement member 881 is thus prevented from tilting even if the urgingforce of the urging members 135 acts on the driven-side rotational body710 such that the engagement member 881 is pressed by the flange 770. Asa result, the engagement member 881 is held at the reference position,thus maintaining engagement between the engagement member 881 and theflange 770. This restricts movement of the driven-side rotational body710 from the decoupled position to the coupled position. That is, evenwhen the driven-side rotational body 710 is arranged at the decoupledposition and rotated by inertial force and, in this state, the pin 860is moved to the connecting portion of the annular groove 740 such thatthe pin 860 becomes separate from the side surface of the groove 720(the side wall 741 of the annular groove 740), the one-way lockingportion 880 restricts shifting of the driven-side rotational body 710.The pin 860 is thus held in the annular groove 740.

To switch the clutch 800 from the disengaged state to the engaged state,the actuator 150 is operated to retract the pin 860 of the lockingmember 850 from the annular groove 740 of the groove 720. This alsocauses disengagement between the engagement member 881 and the flange770. The driven-side rotational body 710 is thus moved to the coupledposition by the urging force of the urging members 135. As a result, thedriven-side rotational body 710 and the drive-side rotational body 110become coupled to each other, thus switching the clutch 800 to theengaged state.

The fifth embodiment achieves advantages equivalent to the advantage (1)of the first embodiment and the advantage (6) of the fourth embodiment.

The clutch according to the present disclosure is not restricted to theconfigurations illustrated in the above-described embodiments but may beembodied in, for example, the forms described below, which aremodifications of the embodiments.

In the first embodiment, the depth of the annular groove 420 is small inthe vicinity of the starting end 421 relative to the depths of the otherportions in the circumferential direction of the driven-side rotationalbody 120. The depth of the helical groove 410 becomes gradually greaterfrom the starting end 411 to the finishing end 412. However, the depthof the annular groove or the depth of the helical groove may be uniformin the circumferential direction. That is, the step between the annulargroove and the helical groove may be set to a uniform size in thecircumferential direction of the driven-side rotational body 120.

In the second embodiment, the protrusion is formed over the entirelength of the connecting portion of the groove. The opposite ends of theprotrusion reach the non-connecting portion. However, if the protrusionis formed at least over the entire length of the connecting portion ofthe groove, shifting of the pin into the helical groove can berestrained by engaging the protrusion with the recess of the pin overthe entire length of the connecting portion. The opposite ends of theprotrusion thus do not necessarily have to reach the non-connectingportion. For example, only one of the end portions may reach thenon-connecting portion. Alternatively, the length of the protrusion maybe equal to the length of the connecting portion such that neither endportion reaches the non-connecting portion. Further, as long as shiftingof the pin from the annular groove into the helical groove is restrainedand disengagement of the clutch is restrained, the protrusion does notnecessarily have to extend over the entire length of the connectingportion. For example, the protrusion may be provided in a portion of theconnecting portion of the groove.

In the third embodiment and its modification, the recessed groove isformed over the entire length of the annular groove. However, therecessed groove only has to be formed at least over the entire length ofthe connecting portion of the annular groove. That is, if the protrusionis formed at least over the entire length of the connecting portion,shifting from the annular groove into the helical groove is restrained.Further, if shifting of the pin from the annular groove into the helicalgroove is restrained and disengagement of the clutch is restrained, therecessed groove may be formed in a portion of the connecting portion.

In the fourth and fifth embodiments, the flange is formed over theentire circumference of the outer circumferential surface of thedriven-side rotational body. However, if shifting of the pin from theannular groove into the helical groove is restrained and disengagementof the clutch is restrained, the flange does not necessarily have toextend over the entire circumference but may be arranged in a portion ofthe outer circumferential surface to extend in the circumferentialdirection of the driven-side rotational body.

The number of the urging members may be modified as needed. For example,a single urging member may be employed to urge the driven-siderotational body.

Any suitable urging member may be employed as long as the urging memberurges the driven-side rotational body toward the coupled position. Theurging member is thus not restricted to the aforementioned compressioncoil spring. For example, a tension spring for pulling the driven-siderotational body toward the coupled position may be employed as theurging member.

The actuator is not restricted to the self-holding type solenoid but maybe, for example, a solenoid having a locking member that is insertedinto a groove only when a coil is energized. In this configuration, theclutch is disengaged only when the coil is energized. The clutch is thusmaintained in the engaged state if the coil cannot be energized. As aresult, even when the actuator fails to operate normally, the pump canbe operated.

The actuator is not restricted to a solenoid. That is, any othersuitable actuator than the solenoid, such as a hydraulic type actuator,may be used to selectively insert and retract the locking member. Alsoin this case, the clutch is disengaged through engagement between agroove of the driven-side rotational body and the locking member. Theforce needed to disengage the clutch is thus obtained from rotationalforce of the driven-side rotational body. As a result, disengagement iscarried out by small force.

The clutch is not restricted to the configuration in which drive forceis transmitted through the balls. The clutch may be a pressing typeclutch.

For example, opposed surfaces of the driven-side rotational body and thedrive-side rotational body may be parallel tapered surfaces eachinclined with respect to the axial direction. The tapered surfaces serveas pressing surfaces. By moving the driven-side rotational body in theaxial direction and pressing the pressing surfaces against each other,the driven-side rotational body and the drive-side rotational body arecoupled to each other.

In the clutch of each of the illustrated embodiments, the shapes of thecomponents are not restricted particularly to the shapes of theillustrated embodiments, as long as the operation illustrated for eachembodiment is ensured. For example, as illustrated in FIG. 14, ballaccommodating grooves 927 may be formed in a large diameter portion 922of a driven-side rotational body 910 and recesses 928 may be formed bylightening portions that lack the ball accommodating grooves 927. Thisdecreases the weight of the driven-side rotational body 910 and thusreduces the inertial force caused by the driven-side rotational body910. As a result, when the driven-side rotational body 910 reaches adecoupled position, rotation of the driven-side rotational body 910quickly stops.

In each of the illustrated embodiments, the clutch switches the state ofpower transmission from the crankshaft to the pump. However, the clutchaccording to the present disclosure may be employed as a clutch arrangedbetween other auxiliary devices, such as a compressor or an oil pump,and the crankshaft. Also, the clutch according to the present disclosureis not restricted to the clutch for switching the state of powertransmission from the crankshaft but may be used as a clutch forswitching the state of power transmission from other drive sources.

1. A clutch comprising: a drive-side rotational body; a driven-siderotational body movable in an axial direction of the drive-siderotational body between a coupled position at which the driven-siderotational body is coupled to the drive-side rotational body and adecoupled position at which the driven-side rotational body is decoupledfrom the drive-side rotational body; an urging member that urges thedriven-side rotational body from the decoupled position toward thecoupled position; a groove formed in an outer circumferential surface ofthe driven-side rotational body, wherein the groove has a helicalportion that extends about an axis of the driven-side rotational bodyand an annular portion that is formed continuously from the helicalportion and extends over an entire circumference of the driven-siderotational body and perpendicularly to the axial direction; a pin thatis selectively inserted into and retracted from the groove andrestricted from moving in the axial direction, wherein, when the pin isin a state inserted in the helical portion and engaged with a side wallof the helical portion, the position of the pin is shifted from thehelical portion to the annular portion through rotation of thedriven-side rotational body such that the driven-side rotational body ismoved to the decoupled position against urging force of the urgingmember; and a restricting portion that restricts shifting of theposition of the pin from the annular portion to the helical portion whenthe pin is in a state located in the annular portion.
 2. The clutchaccording to claim 1, wherein the helical portion is a helical groove,the annular portion is an annular groove having a depth greater than thedepth of the helical groove, the groove includes a step in a connectingportion by which the helical groove and the annular groove are connectedto each other, and a side wall of the step functions as the restrictingportion.
 3. The clutch according to claim 1, wherein the helical portionis a helical groove, the annular portion is an annular groove includinga connecting portion connected to the helical groove, and therestricting portion includes a protrusion and a recess, wherein theprotrusion projects from a bottom surface of the annular groove andextends at least over an entire length of the connecting portion in theextending direction of the annular groove, and the recess is formed at adistal end of the pin and becomes engaged with the protrusion when thepin is arranged in the connecting portion.
 4. The clutch according toclaim 1, wherein the helical portion is a helical groove, the annularportion is an annular groove including a connecting portion connected tothe helical groove, and the restricting portion includes a recessedgroove and a projection, wherein the recessed groove is formed in abottom surface of the annular groove and extends at least over an entirelength of the connecting portion in the extending direction of theannular groove, and the projection projects from a distal end of the pinand becomes engaged with the recessed groove when the pin is arranged inthe connecting portion.